This study evaluates the relationships between human immune response genes, atopic allergy, the third phosphoglucomutase locus and the vigor of the immune response to several antigens. This protocol has been expanded to include RFLP typing in the Molecular Genetics Laboratory. The aim of this protocol is to study 100 nuclear families for chromosome 6 markers (HLA-A, HLA-B, HLA-C, HLA-DR, C2, C4A, C4B, Bf, and Gio), Gm and Km, and relate the polymorphisms at these loci to clinical ragweed sensitivity.